Stent having radially expandable main body

ABSTRACT

A stent made of a material having a low strength and having a main body circumscribing a cylindrical shape and radially expandable from a contracted starting position into a dilated support position, comprising a) a plurality of support segments disposed around the circumference and arrayed on one another in the axial direction each segment being formed by a strut meandering in its coarse structure in its contracted starting position and having alternately opposing meandering curves expandable into the support position made of flexible material; b) a plurality of axial connectors connecting between zenith points of at least a part of the meandering curves in the axial-parallel direction of the support segments; and c) at least one means for stabilizing the strut coarse structure in its contracted starting position against radial expansion and being automatically detachable upon a radial expansion of the stent.

PRIORITY CLAIM

This patent application claims priority to German Patent Application No.10 2007 015 670.9, filed Mar. 31, 2007, the disclosure of which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to expandable vascular stents.

BACKGROUND

One example of a vascular implant is described in detail inInternational Patent Publication No. WO 2004/103 215 A1, in particular,in regard to the fundamental areas of application of such stents and thespecial problems upon use of materials having a low ductile yield andalso lower strengths, such as magnesium alloys.

In the embodiment which may be inferred from this publication, the stentis implemented by a main body circumscribed by a cylindrical shape andradially expandable from a contracted starting position into a dilatedsupport position which, on one hand, comprises multiple support segmentsrunning around the circumference and arrayed in the axial direction onone another. The support segments are each formed by a strut which ismeandering in coarse structure in its contracted starting positionhaving alternating opposing meandering curves made of flexible material.On the other hand, the main body has axial connectors running in theaxial-parallel direction which connect the support segments betweenzenith points of at least a part of the meandering curves.

The above-mentioned magnesium alloys as the material for producingstents have significantly lower strength values than typicalconstruction materials for balloon-expandable stents, such as medicalsteel having the material identifications 316L, MP35N or L 605. Theselower strength values cause problems in the practical application of thestents. It is thus necessary for the stent placement to mount the stenton a balloon catheter. For this purpose, the stent, which is structuredfrom a sleeve material by laser cutting, for example, is crimped ontothe balloon catheter in its contracted starting position. The stent isalso guided on the catheter system through curved areas of the insertionor blood vessel system in this state during the implantation. Individualstruts of the stent may open in the corresponding passages, by which theretention forces of the stent on the catheter are reduced. This causes asignificant risk of loss of the stent.

Especially endangered areas of the stent are the terminal strut elementshaving their meandering curves. In addition, the danger arises due toprojecting edge segments, the so-called “flaring,” that, in addition tothe mechanical irritation of the internal vascular wall upon passage ofthe stenosis or the retraction into the insertion catheter, unintendedstripping of the stent from the balloon catheter will occur.

SUMMARY

The present disclosure describes several exemplary embodiments of thepresent invention.

One aspect of the present disclosure provides a stent made of a materialhaving a low strength and having a main body circumscribing acylindrical shape and radially expandable from a contracted startingposition into a dilated support position, comprising a) a plurality ofsupport segments disposed around the circumference and arrayed on oneanother in the axial direction, each segment being formed by a strutmeandering in its coarse structure in its contracted starting positionand having alternately opposing meandering curves expandable into thesupport position made of flexible material; and b) a plurality of axialconnectors connecting between zenith points of at least a part of themeandering curves in the axial-parallel direction of the supportsegments; and c) at least one means for stabilizing the strut coarsestructure in its contracted starting position against radial expansionand being automatically detachable upon a radial expansion of the stent.

One feature of the present disclosure provides a stent of the typeaccording to the species in such a manner that unintended expansion ofthe entire stent or exposed areas thereof, such as the terminal frontedges, is reliably prevented during the implantation.

This feature is achieved according to the present disclosure by a meansfor stabilizing the strut coarse structure in its contracted startingposition against radial expansion which are integrated in the stentdesign. These stabilization means are then detachable automatically uponthe actual radial expansion of the stent.

These stabilization means advantageously secure radial locking of thestent in its crimped state so that unintended expansion of the stent,even in partial areas, is avoided because of this fixing.

According to preferred embodiments of the present disclosure, thesestabilization means may be implemented in different ways, for example,by detachable glued joints between adjacent meandering curves of a strutor from strut to strut, by catch elements in the stent structure,boundary fixing traverses or by fine structure struts against the cited“flaring.” More detailed explanations may be inferred from the followingdescription, in which exemplary embodiments of the subject matter of thepresent disclosure are explained in greater detail on the basis of theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present disclosure are described hereinbelow withreference to the accompanying figures.

FIG. 1 is a perspective view of one exemplary embodiment of a stent inits contracted starting position having a terminal glued joint as thestabilization means;

FIG. 2 is a detail top view of the stent in an unwound view having aglued joint variant;

FIG. 3 is a detail top view of the stent in an unwound view having adifferent glued joint variant;

FIG. 4 is a schematic detail excerpt in an unwound illustration of thestent having catches as the stabilization means;

FIG. 5 is a schematic detail excerpt in an unwound view of a stenthaving a boundary fixing traverse;

FIG. 6 is a schematic detail excerpt in an unwound view of an exemplaryembodiment of a stent having a different boundary fixing traverse;

FIG. 7 is a schematic detail view in an unwound view of an exemplaryembodiment of a stent having boundary fine structure struts as thestabilization means;

FIG. 8 is an enlarged detail excerpt as shown in FIG. 7;

FIG. 9 is a perspective partial illustration of an exemplary embodimentof a stent having extension struts for removable fastening to a ballooncatheter;

FIG. 10 is a top view of the stent as shown in FIG. 9 in an unwoundview;

FIG. 11 is a detail top view of an exemplary embodiment of a stent in anunwound view having marker projections coupled to one another; and

FIG. 12 is a detail top view of an exemplary embodiment of a stent in anonline view having marker projections coupled in a ring.

DETAILED DESCRIPTION

FIG. 1 clarifies the structure of the stent in its contracted startingposition. The stent is worked out of a cylindrical metal body by lasercutting in such a manner that the stent has multiple support segments 1running around the circumference U and arrayed in the axial direction Aon one another, which are each formed by one of the struts 2 meanderingin their coarse structure in the contracted starting position shown.

In the direction parallel to the axial direction A, the support segments1 are connected to one another by axial connectors 4, which each runbetween the zenith points 5 of meandering curves 3 to be connected. Theaxial connectors 4 always run from the exterior side of a meanderingcurve 3 to the interior side of the meandering curve 3 of the adjacentstrut due to the offset of the adjacent support segments 1 around thecircumference U.

As is not shown in greater detail in the drawings, upon radial expansionof the stent, the sections of the meandering curves 3 running betweenthe zenith points 5 are deployed around the circumference U. The closerthe corresponding sections approach to the circumference U, the greaterthe so-called collapsing pressure of the stent.

To achieve the additional radial fixing of the stent desired accordingto the present disclosure, in the variants shown in FIGS. 1-3, a gluedjoint 6 is provided which may be applied between the two terminalmeandering curves 3 on diametrically opposite radial positions in theform of a grouting point, for example. This glued joint 6 is shownschematically in FIG. 2. With this type of glued joint 6, the adhesivefaces are loaded by tension.

In another exemplary embodiment, it is also possible to attach the gluedjoint 6 in such a manner that the adhesive faces are loaded by shear, asindicated in FIG. 3.

The individual points of the glued joint 6 may not only be situatedterminally, as shown in FIGS. 1-3, but also distributed on thecircumference over the length of the stent 1. With such multiplepositioning, upon radial expansion of the stent, the fixing is detachedautomatically in chronological sequence in accordance with the retentionforce. Experiments have shown that in spite of asymmetrical detachmentof the individual fixed points, the stent may be open homogeneously ifthe fixing force is only large enough that the axial connectors 4 arestill capable of absorbing it. If glued joints 6′ are positioned in thearea of the particular strut 2 second from the outside, for example, theaxial connectors 4 may also act on the glued joint 6′ from both sideswhich favors homogeneous opening behavior. In this case, the outermoststrut 2 is either to be as short as possible or have the fine structuresdescribed in greater detail on the basis of FIGS. 7 and 8 on the edge tosuppress flaring.

FIG. 4 shows a further exemplary embodiment for the stabilization meansfor additional radial fixing of the stent. Two neighboring meanderingcurves 3 of a strut 2 are coupled to one another in the contractedstarting position at their edges by hooked catch elements 7, 8. When thestent is transferred into its contracted starting position, theso-called crimping, the catch elements 7, 8 are engaged with oneanother. The stent is thus held together at its edge, so that the“flaring” cited hereinabove is avoided. During the radial expansion, theengagement between elements 7, 8 is broken open and the stent may openhomogeneously.

In a further exemplary embodiment, the configuration of catch elementsin the form of hooked projections 9, 10 in the interior of a meanderingcurve 3 is shown by dashed lines in FIG. 4. This fixing is also producedduring crimping by hooking of the projections 9, 10 and broken uponexpansion of the stent. It is recognizable that the hooked projections9, 10 may be provided on arbitrary struts 2 along the stent.

FIGS. 5 and 6 show further exemplary embodiments of the stabilizationmeans for the additional radial fixing of the stent in the crampedstate. In these embodiments, fixing traverses 11 shaped in one piece onthe boundary struts 2 are provided which connect to the adjacentmeandering curves 3 of a strut 2 from zenith point 5 to zenith point 5.While only one fixing traverse 11 is provided in FIG. 5, in theexemplary embodiment shown in FIG. 6, the boundary of the stent iscompletely terminated by a row of fixing traverses 11.

Each fixing traverse 11 has a double-arched course having a central bend12 which acts as the intended breakpoint upon radial expansion of thestent. The stent, as already described in connection with the gluedjoint 6, may expand homogeneously by the tearing of the fixing traverses11.

A further exemplary embodiment of the stabilization means providedaccording to the present disclosure is shown in FIGS. 7 and 8. These areperipheral fine structure struts 14 on the boundary at the ends 13 ofthe stent, which are bound to the exterior sides 15 of the meanderingcurves 3. These fine structure struts 14 are formed in each case by twostruts 16, 17 running essentially parallel having coupling struts 18running in the axial direction. The basic configuration of the finestructure struts 14 is thus ladder-like, the double struts 16, 17 beingfolded in a zigzag in the lateral plane of the stent. Curved groinpoints 19 are shaped into the double struts 16, 17 in the bend points,via which the coupling struts 18 may be fastened in one piece whileprotecting the material in regard to the radial expansion of the finestructure struts 14 at the struts 16, 17. The expandability of the finestructure struts 14 is improved by the curved shape in these groinpoints 19.

As schematically indicated in FIG. 8, the fine structure struts 14 inthe area of the interior groin points 19, which are adjacent to oneanother in the contracted starting position, are additionally fixed by aglued joint 6 or also catch means (not shown here), for example. Theentire stent is thus stabilized on its front-side boundary in thecrimped configuration in such a manner that flaring is kept as small aspossible. Due to the fixing at the interior groin points 19, the openingforces act on both sides of this fixing, so that higher fixing forcesmay be overcome without impermissibly distorting the stent structure.

A further exemplary embodiment of the stabilization means for additionalradial fixing of the stent is illustrated in FIGS. 9 and 10. These areextension struts 20, which run essentially in the axial direction A andare bound to the strut at one end via an intended breakpoint 21 to theexternal strut 2. The free end 22 of the extension struts 20 ispermanently fastened in each case in a suitable maimer to a ballooncatheter 23, only schematically indicated in FIG. 9.

The extension struts 21 again counteract a radial expansion of themeandering curves 3 of the external struts 2, in particular, whichsuppresses flaring. Upon dilation of the stent, the intended breakpoints21 are torn and the stent is thus released from the extension struts 20.

Exemplary embodiments for stabilization means against flaring shown inFIGS. 11 and 12 use the x-ray marker projections 24 often present instents, which are formed as eye-shaped projections onto the meanderingcurves 3 of the external struts 2 and are provided with athermoplastically moldable marker polymer coating 25. To use theseelements, which are known in stents, as stabilization means againstflaring, the x-ray marker projections 24 having their marker polymercoating 25 are designed in such a manner that the x-ray markerprojections 24 contact one another after the crimping of the stent andare reshaped into a peripheral ring by a thermal treatment of the markerpolymer coating 25. The ring formation is supported by transverseconnection elements 26 protruding in the peripheral direction from thex-ray marker projections 24, which may be designed as either I-shaped orT-shaped in a top view.

Finally, it is still possible, as shown in FIG. 12, to equip stents withpolymer-coated x-ray marking projections 24 against flaring in such amanner that a peripheral ring made of magnesium, for example, is pushedonto the projections 24 having their coating 25 which is embeddedtherein by heating and brief melting of the marker polymer coating 25and thus fixed. The ring 27 may comprise rigid material or wire, and mayalso be laid on only a partial circumferential length around the stent.

All patents, patent applications and publications referred to herein areincorporated by reference in their entirety.

1. A stent made of a material having a low strength and having a mainbody circumscribing a cylindrical shape and radially expandable from acontracted starting position into a dilated support position,comprising: a) a plurality of support segments disposed around thecircumference and arrayed on one another in the axial direction eachsegment being formed by a strut meandering in its coarse structure inits contracted starting position and having alternately opposingmeandering curves expandable into the support position made of flexiblematerial; b) a plurality of axial connectors connecting between zenithpoints of at least a part of the meandering curves in the axial-paralleldirection of the support segments; and c) at least one means forstabilizing the strut coarse structure in its contracted startingposition against radial expansion and being automatically detachableupon a radial expansion of the stent.
 2. The stent of claim 1, whereinthe at least one stabilization means is formed by a detachable gluedjoint between adjacent meandering curves of one or more struts.
 3. Thestent of claim 2, wherein the glued joint is attached to boundary andinternal struts.
 4. The stent of claim 2, wherein the glued joint isattached in such a manner that the glued joint may be loaded upon radialexpansion by tension or shear.
 5. The stent of claim 1, wherein the atleast one stabilization means is formed by catch elements which interactwith one another on the meandering curves which may be engaged with oneanother upon transfer of the stent into its contracted starting positionand are detachable upon radial expansion of the stent.
 6. The stent ofclaim 5, wherein the catch elements are formed by hook projections onthe meandering curves.
 7. The stent of claim 1, wherein the at least onestabilization means is formed by fixing traverses which connect theboundary meandering curves and may be broken open upon radial expansion.8. The stent of claim 7, wherein the fixing traverses run between zenithpoints of two adjacent meandering curves and have a bend as the intendedbreakpoint.
 9. The stent of claim 1, wherein the at least onestabilization means is formed by a plurality of fine structure strutsperipherally disposed around the boundary of the stent ends.
 10. Thestent of claim 9, wherein the plurality of fine structure struts areimplemented as double struts folded in a zigzag in a lateral plane ofthe stent which are fixed on one another at their adjacent groin pointsin the contracted starting position.
 11. The stent of claim 1, whereinthe at least one stabilization means is formed by a plurality ofextension struts on the stent which detachably connect the boundarystruts to the catheter for placing the stent.
 12. The stent of claim 11,wherein the plurality of extension struts are each bonded to the stentvia an intended breakpoint.
 13. The stent of claim 1, further comprisinga plurality of x-ray marker projections coated via marker polymer on theboundary struts, wherein the at least one stabilization means is formedby x-ray marker projections coupled in a ring via the marker polymercoating in the contracted state.
 14. The stent of claim 13, wherein theplurality of x-ray marker projections are provided with radiallyoriented transverse connection elements.
 15. The stent of claim 13,wherein a ring which is embedded in the marker polymer coating is drawnonto the x-ray marker projections in the contracted stent state.